Equipment life extension involves upgrades

Every plant wants to get more service life from site
machinery. Since about 1990, quite a number of start-up
consulting companies have formed to advise clients on equipment
life extension. These companies use different approaches: some
apply large-scale, computer-based statistical methods, while
others blend traditional estimates with risk-based analysis.
All of these approaches have merit, but none of them can
provide all of the answers with high precision. The key
ingredients of any useful endeavor include reviewing the
assets past failure history, examining nondestructive
testing (NDT) data, and upgrading the weakest link.

Failure history counts

Wherever failure history exists and the failures root
causes were analyzed, authoritative answers on remaining
service life are possible. The same can be said for thoroughly
evaluating NDT data, which can provide focus to determine
remaining life.

On stationary equipment and piping, wall thickness is of
great importance. Loss of material decreases the allowable
pressure rating. Corrosion and erosion can lower the safety of
the equipment; thus, continued operation becomes risky.
Thickness changes often occur at locations, such as elbows,
where fluid flow changes direction. Changes in velocity such as
at valves or near restrictions are of high interest. Some can
be investigated with NDT methods, which certainly include X-ray
imaging, among others. The extent of fluid-dependent corrosion
can be estimated from coupons placed in piping and vessels.

Pumps. For pumps, failure history and past
repair data must be matched with a thorough understanding of
upgrade measures that have been taken by successful
best-of-class organizations. Advanced lube
application will probably be part of it, as will the extension
of oil replacement intervals now possible by synthetic
lubricants and advanced bearing housing protection
measures.

To what extent superior bearings (ceramic hybrids) are of
value must be determined on a pump-by-pump basis. Perhaps a set
of angular bearings with unequal contact angles should be
installed in your problem pumps. The symmetrical sets of
angular contact bearings mentioned in the most widely used pump
standard may not perform adequately. The extent that superior
sealing technology (dual seals, as shown in
Fig. 1) provides more value must be determined
on a service-by-service basis. As a general rule, the
industrys view about dual seals deserves to be
reassessed. Sealing technology has made considerable
progress in the past two decades. Virtually all present-day
seals are cartridge-style configurations, and braided packing
is being displaced by mechanical seals in the hydrocarbon processing industry (HPI), as
well as in the power generation and mining industries.

Fig. 1. Dual mechanical seal
in a
slurry pump. The space between the
sleeve and the inside diameter of the
two sets of seal faces is filled with a
pressurized barrier fluidusually
clean water. Source: AESSEAL Inc.,
Rockford, Tennessee, and
Rotherham, UK.

However, not all manufacturers of mechanical seals use the
same acceptance test procedure for their products. A widely
applied industry standard stipulates using air as a test gas
for mechanical seal tightness. Of course, these seals are
ultimately intended for safe containment of flammable, toxic or
otherwise hazardous liquids. While the standards
expectation is that leakage from these seals does not exceed
5.6 gm/hr, recent tests showed that merely following this easy
testing routine can actually allow orders of magnitude more
liquid to escape. It is, therefore, advisable to question seal
vendors on the matter and to purchase only products that meet
the purchasers safety and reliability requirements. We all
want seals to leak no more than 6.5 gm/gr when first installed
on pumps.

Lubrication systems

Lubricant application and standby bearing preservation are
especially important in humid coastal climates and in
dust-laden desert climates. Oil mist is the answer. The
settling of foundations and pipe supports should be addressed.
For steam turbines, the blade stresses and water quality must
be compared with those units in successful long-running
installations elsewhere.

In gearboxes, the remaining service life is largely examined
by tooth loading (stresses on tooth face) and temperature
measurements. In all instances, synthetic oils from the most
experienced oil formulators will greatly extend gear life. Oil
additives are everything. They drive both cost and service
life. Oil cleanliness is equally important.

Certain warehouse spares (gears, electric motors, etc.)
should be upgraded, if important. If doing so, it is likely to
speed up re-commissioning after an unanticipated future
shutdown.

Compressors

For compressors, engineers should consider the mentioned
points. Valve technology and piston velocity are important
comparison-worthy parameters on reciprocating compressors.
Onstream performance tracking and prior sealing technology are important for
centrifugal compressors, etc. They determine seal system
upgrade potential. Never overlook couplings and the work
procedures used to attach couplings to shafts. They tell a lot
about remaining run length.

Consultants

Whether one ultimately receives life extension guidance from
individual consultants or from billion-dollar consulting giants
with applicable experience is of no consequence, as long as
there is the one common thread: Determining where upgrades are
possible. Upgrades are critical to imparting longer life to
existing equipment, and they can often be accomplished at
relatively low cost. Assessments of remaining life should
include detailed advice on how to upgrade weak links, which
implies:

In short, the entity involved in advising you on equipment
life extension must understand the feasibility of component
upgrades. Component upgrading is one of the keys to life
extension and deliverables that should be contractually agreed
upon with the upgrade provider. Be sure that the consulting
company youve asked to give advice on equipment life
extension includes these deliverables. HP

The author

Heinz P. Bloch resides in
Westminster, Colorado. His professional career
commenced in 1962 and included long-term assignments
as Exxon Chemicals regional machinery
specialist for the US. He has authored over 520
publications, among them 18 comprehensive books on
practical machinery management, failure analysis,
failure avoidance, compressors, steam turbines,
pumps, oil-mist lubrication and practical lubrication
for industry. Mr. Bloch holds BS and MS degrees in
mechanical engineering. He is an ASME Life Fellow and
maintains registration as a Professional Engineer in
New Jersey and Texas.

Have your say

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I believe it is essential to reduce or eliminate the 'bad actor' equipment items to achieve 'best in class' safety and reliability. There is always a reason for 'bad actors', and unless that core reason is determined and correctly dealt with, the problem remains and failures will repeat. A thorough engineering analysis may be necessary to correctly identify and correctly mitigate the core problem causing the failures.

Statistical analyses are not useful for evaluating a piece of equipment. The ACTUAL HISTORY of the particular equipment should be the reference, not 'statistics.' Each equipment installation is unique in the details, a first of a kind in reality. Details are important.